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Related Concept Videos

ECG Interpretation of Arrhythmias II: Atrial, Junctional and Ventricular Arrhythmias01:25

ECG Interpretation of Arrhythmias II: Atrial, Junctional and Ventricular Arrhythmias

Arrhythmia is a condition characterized by an irregular heart rhythm, with ECG changes that differ based on its origin and nature. The types of arrhythmias discussed below include atrial, junctional, and ventricular arrhythmias.Atrial ArrhythmiasPremature Atrial Complexes (PACs): PACs are early atrial beats caused by stress, caffeine, alcohol, electrolyte imbalances, hypoxia, hyperthyroidism, or certain medications (e.g., bronchodilators and decongestants). The ECG shows early P waves with an...
Dysrhythmias IV: Characteristics of Bradyarrhythmias01:18

Dysrhythmias IV: Characteristics of Bradyarrhythmias

Bradyarrhythmias are cardiac rhythm disorders characterized by a slower-than-normal heart rate, typically defined as fewer than 60 beats per minute. Some of which are discussed here:Sinus BradycardiaSinus bradycardia presents a heart rate lower than 60 beats per minute, with a regular rhythm originating from the SA node. The ECG typically shows normal P waves preceding each QRS complex, a normal PR interval (0.12 to 0.20 seconds), and a normal QRS duration (0.06 to 0.10 seconds).First-Degree AV...
Electrophysiology of Normal Cardiac Rhythm01:19

Electrophysiology of Normal Cardiac Rhythm

The normal cardiac rhythm is a synchronized electrical activity that facilitates the regular and coordinated contraction of the heart muscle. This process is essential for efficient blood circulation throughout the body. The fundamental elements involved in establishing and maintaining this rhythm include the unique electrical properties of cardiac muscle cells, the sinoatrial (SA) node's pacemaker function, the specialized conducting system, and the ionic mechanisms underlying each phase of...
Disturbances in Heart Rhythm01:29

Disturbances in Heart Rhythm

Arrhythmia or dysrhythmia refers to an abnormal heart rhythm caused by a defect in the heart's conduction system. It can cause the heart to beat irregularly, too quickly, or too slowly, leading to symptoms like chest pain, shortness of breath, and fainting. Factors such as stress, caffeine, alcohol, nicotine, cocaine, certain drugs, congenital defects, diseases, and electrolyte abnormalities can trigger arrhythmias.
Arrhythmias are categorized by their speed, rhythm, and origin. A slow heart...
Dysrhythmias III: Characteristics of Dysrhythmias01:29

Dysrhythmias III: Characteristics of Dysrhythmias

Dysrhythmias, also known as arrhythmias, are irregular heart rhythms that result from abnormal electrical activity in the heart, affecting its ability to circulate blood efficiently. Tachyarrhythmias, a subset of dysrhythmias, are characterized by abnormally fast heart rates exceeding 100 beats per minute. Here are some types of tachyarrhythmias with their distinct ECG features:Sinus Tachycardia:Sinus tachycardia presents a regular heart rhythm with an increased rate of 101-180 beats per minute.
ECG Interpretation of Rhythms01:24

ECG Interpretation of Rhythms

An electrocardiogram (ECG)graphically represents the heart's electrical activity on ECG paper or a monitor.
Components of the Electrocardiogram
The primary components of a normal ECG waveform in Normal sinus rhythm(NSR) include the P wave, PR interval, QRS complex, ST segment, T wave, and occasionally a U wave.
ECG waveforms are divided by vertical and horizontal lines at standard intervals.
The horizontal axis measures time and rate, and the vertical axis measures amplitude or voltage. When...

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Related Experiment Video

Updated: May 22, 2026

Benefits of Cardiac Resynchronization Therapy in an Asynchronous Heart Failure Model Induced by Left Bundle Branch Ablation and Rapid Pacing
12:45

Benefits of Cardiac Resynchronization Therapy in an Asynchronous Heart Failure Model Induced by Left Bundle Branch Ablation and Rapid Pacing

Published on: December 11, 2017

When QTc Shrinks After Rhythm Conversion.

Mohammed Hussein Kamareddine1, Alyssa Zakala1, Farid Farkouh1

  • 1Lankenau Medical Center, Main Line Health, Wynnewood, Pennsylvania, USA.

JACC. Case Reports
|May 21, 2026
PubMed
Summary
This summary is machine-generated.

QT hysteresis can cause a temporary shortening of the corrected QT (QTc) interval, even with QT-prolonging medications. This phenomenon impacts the interpretation of electrocardiograms during antiarrhythmic treatment.

Keywords:
QT hysteresisQTc shorteningamiodaroneantiarrhythmic therapy

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Area of Science:

  • Cardiology
  • Electrophysiology
  • Pharmacology

Background:

  • Atrial fibrillation is a common arrhythmia often managed with antiarrhythmic drugs.
  • Amiodarone is a frequently used antiarrhythmic agent known for its potential to prolong the QT interval.
  • Cardioversion is a procedure to restore normal heart rhythm.

Purpose of the Study:

  • To report a case of transient QTc shortening after cardioversion in a patient on amiodarone.
  • To highlight the phenomenon of QT hysteresis and its clinical implications.

Main Methods:

  • A case report of an 83-year-old male patient with atrial fibrillation.
  • Direct-current cardioversion was performed to restore sinus rhythm.
  • Post-procedure electrocardiography was analyzed for QT interval duration.

Main Results:

  • Successful restoration of sinus rhythm post-cardioversion.
  • An unexpectedly short corrected QT (QTc) interval of 344 ms was observed.
  • This was attributed to QT hysteresis, a delay in ventricular repolarization adaptation.

Conclusions:

  • QT hysteresis can lead to transient QTc interval shortening.
  • This finding is crucial for accurate interpretation of QT intervals during antiarrhythmic therapy.